Heaters such as process heaters and furnaces are commonly used for heating a feedstock in hydrocarbon processes such as reforming, cracking, catalyst regeneration, dehydrogenation, and others. Example heaters include a firebox having firing walls extending along the length of the firebox, and end walls disposed at ends of the firebox. A heater coil includes a plurality of process tubes that are disposed within the firebox. The process tubes are arranged along a line parallel to the firing walls in the firebox chamber. A feedstock, e.g., a hydrocarbon feedstock, passes through the inlet manifold, through the process tubes, and through the outlet manifold. The process tubes are exposed to radiant heat generated from burners. The burners typically are arranged along the firing walls.
In operation, the feedstock is introduced to the process tubes through the inlet manifold. The feedstock is heated as it flows through the process tubes to provide a product. In a cracking process, for example, the heated feedstock is thermally cracked to provide a cracked gas product, which exits through the outlet manifold.
To improve yield and selectivity, among other advantages, it is useful to form the process tubes in a U-shape. The U-shaped process tubes conventionally have a small diameter, and typically are suspended within the heater. However, with conventional heater coils, burners need to supply heat to both the outside and the inside of the process tubes for uniform heating. The performance of such burners can be unpredictable, and can result in excessive nitrogen oxide (NOx) emissions.
Therefore, there remains a need for effective and efficient apparatuses and processes for heating a feedstock.